Artificial line



P 1931- A. w. HORTON, JR 1,799,794

ARTIFICIAL LINE Filed NOV. 21, 1928 2 Sheets-Sheet l If H6. 8. 2/ 2/ M //v VENTDR A. W Hanrou JR.

A TTOHNEY April 7, 1931. A. w. HORTON, JR 1,799,794

ARTIFICIAL LINE Filed Nov. 21, 1928 2 Sheets-Sheet 2 fie. l0. 4

//v I/ENTUIF A. W HURT-0A1. JR.

A TTOFI'NE Y Patented Apr. 7, 1931 UNITED srAres PATENT OFFICE ARTHUR HORTON, JR., OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO BELL TELE- PHONE LABORATORIES, NEW YORK ARTIFICIAL LINE 'l-"NCORPORATED, OF NEVI YORK, N. Y., A. CORPORATION OF Application filed November 21, 1928. Serial No. 320,858.

This invention relates to artificial lines and particularly to artificial lines for simulating the transmission properties of lines having uniformly distributed constants.

he object of the invention is to provide artificiallines of the'recurrent type having the property that their characteristic impedances are similar to the characteristic impedances of asmooth line, and, by proper ad 0 ustlnent ofthe'values of the component impedances, may be made equal to the characteristic impedances of a given smooth line. Such lines may he used for balancing a smooth line, asin the operation of telephone repeaters, or in duplex tele raph systems and a highly accurate balance may be obtained, provided both lines are of sufficient length or are so terminated that wave reflection from their remote ends is negligibly small.

Artificial lines having the above noted property are disclosed in U. S. patent to G. A. Campbell No. 1,643,332, dated September 27, 1927, these lines being of the lattice or bridge type contemplated by the present invention and having as their component branch impedancesresistive inductances and conductive condensers in accordance with the usual method of separatingthe component impedances of a uniform line.

In the improved lines of'the present invention lattice sections are used comprising impedance branches having elements of only two types, namely, resistances and condensers or resistances and inductance coils. A feature ofthe invention is that the lattice structures are not symmetrical, the two diagonal branches having unequal impedances.

Referring to the drawings, Figs. 1 to 4 inclusive illustrate previously known forms of ladder type networks;

Fig. 5 is a generalized T section of the forms of Figs. 1 and '2;

Fig. 6 illustrates a generalized lattice or bridge section of a form of the present invention, which is electrically equivalent to the Tin Fig. 5-;

Figs. 7 to 10 inclusive show specific lattice sectionsembodying the invent-ion;

Fig. 11 illustrates ageneralized form of the 71' type sections of Figs. 3 and 4; and

Figs. 12 and 13 illustrate lattice sections embodying theinvention, which can be made equivalent to the 7r section of Fig. 11.

A smooth line is one whose impedance elements are uniformly distributed in character, and is exemplified by non-loaded open wire lines and cables. The characteristic impedance of a smooth line is the impedance measured at the'input terminal of a line of infinite length, or of finite length if the remote end is terminated by an impedance which is equal to'the characteristic impedanoe at all frequencies. The characteristic impedance varies with frequency and is expressed by the formula:

3 G-l-jwc' (1) where Z =the characteristic impedance, R=the resistance in ohms per loop mile; L the inductance in henries per 10013111116 G=the leakage conductance in ohms per loop mile;

C=the capacity in farads per loop mile;

w 2 '17 times the frequency. An inspection of Equation (1) shows that at zero frequencythe characteristic impedance is equal to V E V e while at infinite frequency it is equal to I finite number of sections so that no waves are reflected from the end. In practice, however, it is found that the reflection effects are negligible in a line composed of several sections. A line terminated in the characteristic impedance at the remote end is free from wave reflections regardless of the number of sections used.

In terms of the smooth line constants the elements in Fig. l are:

R RU-LG 2G /1T0 ZOJL O 013 sure (2) The elements in Fig. 2 are:

R melee 22* ZO /ZFG LG* R0 2afgv z (3) The elements in Fig. 3 are:

2L /R G R O L G R82= RU-LG 33 131/23? In Fig. 4: the element-s are:

R ale /L7] LG-R0 2L L0 ifio' 5) The sections in Figs. 1 and 2 are said to have mid-series terminations because the terminating arms are series impedances equal to half the series impedance of a full section, while the sections in Figs. 3 and 4 have mid-shunt terminations because the terminating arms correspond to half the shunt admittance of a full section. The structures in Figs. 1 and 3 are suitable for simulating the impedances of smooth lines in which while the networks in Figs. 2 and i are of use when the relationship obtains. These networks are described in British Patent 223,336 of October 523, 1924, to A. C. Bartlett.

Fig. 5 shows a generalized T network of the form of Figs. 1 and 2 where the arms X represent the series impedance and X the shunt impedance. It may be shown that in general the lattice network of Fig. 6 is completely equivalent to the ladder network of Fig. 5 when X =A (6) and BO-A m-n (7) where A is the impedance of the two line arms of the lattice and B and C are the impedances of the diagonal branches respectively. .Vhen the network of Fig. 5 is of the type shown on Figs. 1 and 2, the impedance X is a resistance and the shunt impedance X may be considered to be composed of two impedances in parallel, one a resistance designated 66X], where a is a con stant, and the other a reactance designated N ow assuming that the impedance B in the network of Fig. 6 is a resistance of value 70X and substituting in Formula (7) the components of X the following equation is obtained:

1 1 2X +IcX +O from which as follows:

A: X1 B=kX lc+ 1 2 [6 X3 a(lc+ 1) Mic-(0 has oneless element. In this case; the element where (he and f are the component elements of the impedance arm G, This network is physically realizable solong as a. The

value of a follows fromthe relationship be valuessof the lattice equivalent of Fig 1 are:

tween R and B in Fig. 1, or between the I 70 corresponding elements in Fig; 2. By sulo- B J a stituting in formulae (11) the Values that X and X have in-the network of Fig. l, the a ZOH/LO' elements of a lattice sectionequivalent to the (a l) RO'LG network of Fig. 1 are determined. The Values are: a:

1 Z A= V f= (14) where B: k F: ROLG O 2LGV 2 m i The network is illustrated in Fig. 9. d The elements of the lattice e uivalent to the R0 LG q T in Fig. 2 for the condition 7a=a, are-:. f R co n 1 Z R 7 9c f J B J? The Value of the coetficient a in this case is zw a2 2G /RG RUVLG 2LG 1 T2 'The structure of the equivalent lattlce sec- 1 6 a (15) tion is shown in Fig; 7.v Where By substituting in formulae (11) the LG 0 Values that X and X have in Fig. 2 and the r. value of a determined from Fig.2 in a man- 2R0 ner siinllar to that for evaluating it from Th t rk i jH t t di Fj 10 Flghl, the following Values are obtained-for I a i il manner-a l tti t k theelements oftheequivalent lattice section: equivalent to type networks f Figs.

i a 3 and 4 may be d etermined. A general form A: E of the 'n' networks is shown in Fig. 11, where v Y represents the series impedance and Y H the shunt impedances of the specific struc- B= k tures. The series impedance Y is separated G V into its components, aresistance, (aY and a reactance Y The lattice will have the d: (k +1) L G RO' same general structure asthat obtained from k ZGJRT a T network, which is represented by Fig. 6.

I The Values of the elements are. then. found g( lc+1) '\/R to be:

G A: 1 V V J p B=ICY2 12o I (70+ 1) where W Y3 LGRG (k+1), Y T P at? 1 2 This section is.illustrated'inFigu8. Y 16 For the special condition, is a, the imf (ka+2k+1) 2 pe ance 6 bec Ine infin di n twork These structures are realizable when 7c a.

When the Values ofY and Y correspond-' ing to Fig. 3 are substituted in Equations (16), the lattice equivalent to Fig. 3 takes the form of Fig. 7 and the element values are:

(Ica+2lc+ n 130* LG 2LG T m The lattice equivalent to the 7r in Fig. 4

has the form of Fig. 8, and the elements are evaluated as follows:

If 7c=a the element 7" becomes zero and there is one less element present. Figs. 12 and 13 illustrate lattice networks obtained from the 71' structures of Figs. 3 and 4; respectively, for the special condition 04 70. In Fig. 12 the elements are:

In Fig. 13 the elements are expressed by:

It is obvious that in general there are an infinite number of lattice networks which may be made equivalent to each T or 7r network, since there are an infinite number of values of is which may be used.

It is furthermore possible to obtain another group of lattice structures identical in con figuration to those already described, by applying a numerical factor to each of the series arms, this operation being compensated for in the bridge arms, whereby the characteristic impedance of the structure at all frequencies remains unchanged. This operation, however, results in the attenuation characteristic differing from that of the original lattice according to the particular value of the numerical factor chosen. In consequence, since there are an infinite number of possible numerical factors there are an infinite number of attenuation characteristics possible in the same type of structure, the characteristic impedance remaining unchanged.

In balancing a smooth line by an artificial line composed of network sections such as are embodied in this invention, the number of sections, in theory, should be infinitely large, to prevent wave reflections at the junction of the two lines. In practice, however, two or three sections are generally found suffieient to afford an accurate balance without serious wave reflections.

What is claimed is:

1. An artificial line for simulating the impedance of a smooth line, composed of recurrent sections of lattice network each section having in series an equal resistive impedance in each side of said line and two bridging impedances, one connecting between an input terminal and an output terminal on opposite sides of said line, the other connecting between the remaining input and output terminals, one of said bridging impedances being purely resistive, the other comprising a single reactive element.

2. An artificial line of recurrent lattice type sections for simulating the impedance of a smooth line, each section comprising a pair of equal resistive branches and a pair of impedance branches interconnecting the terminals of said resistive branches, one of said impedance branches comprising three impedance elements, the other, one impedance element.

3. A lattice network comprising a pair of equal resistive branches disposed in series with the line, and a pair of impedance branches interconnecting the terminals of said resistive branches, one of said branches being a three-element branch comprising two resistance elements and one reactive element, the other consisting of a resistance element, the elements of said section being soproportioned that the characteristic impedance is R 'wL z J L G+jw0 where R, L, G and C are constants.

4. A lattice network comprising a pair of equal resistance branches and a pair ofim-' pedance branches interconnecting the terminals of said resistance branches, one of said impedance branches being resistive, the other being a three-element branch comprising the parallel combination of a resistance and reactance, in series with a resistance, the branches of said network being so proportioned with respect to the constants of a given smooth line that its characteristic impedance is equal to that of said smooth line.

5. A lattice network comprising a pair of equal resistance branches and a pair of impedance branches interconnecting the terminals of said resistance branches, one of said impedance branches being resistive, the other comprising a resistance and reactance in series relation, the branches of said network being so proportioned with respect to the constants of a smooth line that its characteristic impedance is equal to that of said smooth line.

6. Incombination, a smooth line having a characteristic impedance 9 R +jwL 0+ '50 and an artificial line of recurrent lattice sections, each section having a series resistance in each side of the line equal to and two bridging arms interconnecting the terminals of said series resistance, :one of said bridging arms consisting of a resistance, the other being a three-element arm comprising a reactance and two resistances, the elements of said bridging arms being so related to said series resistances that the characteristic impedance of said artificial line is equal to Z in which R is the series resistance of said smooth line per unit length, G the shunt conductance per unit length, L, the series inductance per unit length and C, the shunt capacity per unit length.

7. In combination, a smooth line having a characteristlc lmpedance Z R +j:wL L I G+ T0 and an artificial line of recurrent lattice sections, each section having a series resistance in each side of the line equal to V and two bridging arms interconnecting the terminals of said series resistances, one of said bridging arms consisting of a resistance, the other being a three-element arm comprising a reactance and two resistances, the elements of said bridging arms being so related to said series resistances that the characteristic impedance of said artificial line is equal to Z in which R is the series resistance of said smooth line per unit length, G the shunt conductance per unit length, L, the series inductance per unit length and C, the shunt capacity per unit length.

8. The combination of claim 6 in which said three-element arm is a resistance in series with the parallel combination of a resistance and a reactance.

9. The combination of claim 7 in which said three-element arm is a resistance in series with the parallel combination of a resistance and a reactance.

In witness whereof, I hereunto subscribe my name this 20th day of November, 1928.

' ARTHUR W. HORTON, JR. 

